High-efficiency fan assembly for vacuum cleaner



Aug. 2, 1966 R. MAZEPA 3,263,909

HIGH-EFFICIENCY FAN ASSEMBLY FOR VACUUM CLEANER Filed July 30, 1964 4 Sheets-Sheet 1 v INVENTOR ROBERT MAZEPA BY /Z %j4,m

ATTORNEY Aug 2, i n. MAZEPA 3,253,909

HIGH-EFFICIENCY PAN ASSEMBLY FOR VACUUM CLEANER 4 Shuts-Shoat 2 Fund July 50, 1964 Aug. 2, 1966 R. MAZEPA 3,253,909

HIGH-EFFICIENCY FAN ASSEMBLY FOR VACUUM CLEANER Filed July 30, 1954 4 Sheets-Sheet 5 BLADES ARE. DESIGNED ACCORDING TO A LOGARITHMIC SPIRAL FIG. 8

G= BLADE ANGLE B= DISCHARGE ANGLE I"c=RADIUS OF CURVATURE AT POINT P.

INVENTOR ROBERT MAZEPA ATTORNEY Aug, 2, I966 flied July 50, 1964 R. MAZEPA 3,263,969

HIGH-EFFICIENCY FAN ASSEMBLY FOR VACUUM CLEANER 4 Sheets-Sheet 4 EFFICIENCY /0) INVENTION INVENTION FLOW (ScFmI I- I-Va omncz DIAM. ORIFICE M INVENTOR ROBERT MAZEPA ATTORNFV United States Patent 3,263,909 HIGH-ElFFIClENCY FAN ASSEMBLY FOR VACUUM CLEANER Robert Mazepa, Baltimore, Md., assignor to The Black and Decker Manufacturing Company, Towson, Md., a

corporation of Maryland Filed July 30, 1964, Ser. No. 386,128 5 Claims. (Cl. 230117) The present invention relates to a high-efficiency multistage fan assembly or suction unit for a vacuum cleaner, and more particularly, to a multistage fan assembly which has two salient advantages: one, it is capable of meeting a wide range of vacuum cleaner requirements, ranging, for example, from the requirements of a central vacuum cleaning system to that of a heavy-duty industrial or commercial-type cleaner, such as a furnace cleaner; and secondly, it operates at relatively-higher efficiencies than the prior art devices and has its peak efiiciency falling within the desired operating range.

Prior to this disclosure, vacuum cleaners have been designed and commercialized according to such factors as sealed suction, motor horsepower, or air flow capacity; but at best, these are vague criteria and do not satisfy the theoretical requirements of a vacuum cleaner capable of rendering an outstanding performance. For example, to rate a vacuum cleaner according to sealed suction is virtually meaningless since it is only an indication of static pressure under conditions where no useful work is being performed by the machine. The criterion of motor horsepower, which is currently in vogue, is equally confusing inasmuch as it does not take into account the particular fluid-dynamic design of the fan assembly or air flow system employed in the machine.

The air flow capacity, on the other hand, is an important factor to be considered; provided, however, that it is determined under actual operating conditions, and provided, specifically, that the pressure or suction head is taken into account. The cleaning capability of a vacuum cleaner, sometimes referred to in the art as the pickup power of the machine, is a function of the impulse exerted on the dust particles by the moving air stream, or more precisely, a function of the momentum of the air at the inlet region of the pick-up nozzle. The momentum of the air is a product of mass and velocity, and from a known mathematical derivation, can be shown to be dependent, ultimately, upon the square of the air flow measured in cubic feet per second.

This air flow, however, must be measured under actual operating conditions where the vacuum cleaner is connected to a particular system, as for example, to a given length of hose of a certain diameter with a nozzle carried on the end of the hose; otherwise, the stated air flow has no real meaning. The prior art commercial machines, however, have invariably listed air flow purely as an abstract figure, one which is obtained from measurernents made only on the vacuum cleaner, disassociated from any particular system requirements. Very often, the prior art machines do not have sufficient differential pressure to maintain the desired air flow for a particular system; and hence, the cleaning capability falls off quite drastically in actual usage. Consequently, in analyzing the cleaning capability of a vacuum cleaner, which is the ultimate test, the differential pressure must be taken into account along with the measured air flow for the requirements of any particular system. Generally speaking, a central vacuum system requires relatively-high differential pressures to obtain the necessary air flow; an industrially-rated portable electric vacuum cleaner, on the other hand, requires moderate differential pressures, but conversely, a relatively-high air flow.

3,263,969 Patented August 2,1966

Moreover, the prior art has resorted to fan assemblies involving multistage impellers whose individual vanes or blades are generally selected from respective arcuate portions of a family of circles whose centers are eccentric with respect to the axis of rotation. However, the selection of the generating circle, as well as the particular arcuate portion of it, is generally haphazard and usually involves an empirical cut and try approach. This approach is indeed a poor one and, to date at least, has not resulted in a commercially-practical impeller capable of achieving a theoretically optimum transfer of the mechanical energy of the motor shaft into the energy of the air. The energy in the air comprises a dynamic component and a static component, the former involving the kinetic energy of the air, and the latter involving its pressure energy.

The prior art is also exemplified by the German Patent 23,234, published in 1883, which shows a vacuum cleaner impeller having individual blades constructed according to an Archimedean spiral; and by the United States Patent 2,767,906 issued in 1956, which shows an impeller having individual blade-s constructed according to the involute curve.

In these prior designs, the blade angle-which is defined as the angle between the tangent to the blade at any point and a normal to the radius of rotation at that pointis continually changing from the inlet to the out let of the impeller. With the involute and the Archimedean spiral, the blade angle is continually decreasing; and with the arc of a circle, it is sometimes increasing, sometimes decreasing, depending upon the center of the base circle and the particular radius which is chosen. Because of their continually changing blade angle, these prior art impeller designs fail to accomplish an outimum transfer of energy, that is, from the mechanical energy of the motor shaft to the total energy of the airfor a required combination of pressure and flow. Moreover, these prior blade designs, especially the involute and the Archimedean spiral, are characterized by a relativelyhigh inlet angle and a correspondingly relatively-low discharge angle; hence, the blades are not inherently selfcleaning and have a tendency for dust to accumulate on the inside of the blade, thereby resulting in reduced performance and reduced operating efficiency. Furthermore, the air channels between adjacent blades are relatively long, thereby resulting in greater frictional losses.

Accordingly, it is an object of the present invention to provide a high-efficiency fan assembly for a vacuum cleaner, one which most closely approaches the theoretical parameters of an outstanding unit.

It is another object to match the design of the impellers with that of the stator and other stationary components in order to obtain optimum performance and efficiency from the overall fan assembly.

It is another object to provide a fan assembly which is capable of meeting a wide range of system requirements, such that the vacuum cleaner may be readily used as an industrial or commercially-rated portable unit or else as a fixed suction unit for use in conjunction with a central system.

It is another object to provide a fan assembly which 6 dynamic component, and the pressure energy, a static component.

It is another object to provide an impeller whose individual blades are designed in accordance with a logarithmic spiral generated from a base circle whose center is coincident with theaxis of rotation, the logarithmic spiral design being characterized by a constant blade angle for substantially uniform energy transfer at any radius of rotation.

It is another object to choose one of a family of logarithmic spirals whose angles range from a minimum of 32 degrees to a maximum of 38 degrees.

It is another object to provide each impeller with a tapered side, preferably in the order'of 4, so as to achieve four main purposes: one, to adjust the pressure-flow characteristics to the precise operating range that is desired; two, to obtain an improved operating efi'iciency; three, to reduce back flow at the respective blade tips; and four, to reduce air turbulence between adjacent blades and hence reduce frictional losses. 7

It is another object to provide a molded stator in which a plurality of return-channel blades are formed integrally on one side of the stator, while a plurality of diffuser blades are formed integrally on the opposite side of the stator, thereby resulting, first, in greater compactness and reduced manufacturing cost, and secondly, because of the inherently smooth surface of the molded component, drastically reduced skin frictional losses associated with the air flow.

In accordance with the broad teachings of the present invention, a high-efficiency fan assembly for a vacuum cleaner is herein illustrated and described, which com prises, in combination: a first stage impeller means having a plurality of blades, each of which is designed according to a logarithmic spiral generated from a base circle whose center coincides substantially with the axis of rotation; a first stage diffuser means radially of the first stage rotating impeller means for controlling the rate of energy conversion from dynamic energy into pressure energy with a minimum of loss; a second stage impeller means axially of the return channel means, the second stage impeller means being substantially identical to the first stage; a return channel means for directing the air flow from the first stage diffuser to the second stage impeller; and a second stage difiuser means radially of the second stage impeller means for converting the kinetic energy of the air (or dynamic head) into a pressure head with a minimum of loss involved and with a view to reduce the later losses involved in the discharge of the air through the usual exhaust.

'I he first and second stage impeller means are designed to elfect an optimum transfer of the mechanical energy of the motor shaft into hydraulic (kinetic and pressure) energy of the air; and preferably, each individual blade of the impeller is designed in accordance with a logarithmic spinal characterized by a constant blade angle in the order of 35", which represents an optimum compromise between energy transfer, input power requirements, and control of dust accumulation within the impeller. After being designed in accordance with the 35 logarithmic spiral, each individual blade, if desired, may be approximated as closely as possible by a circular arc, which is chosen purely for reasons of manufacturing convenience; and a family of individual blades is then generated for each impeller.

The first stage diffuser means preferably comprises a vaneless diffuser formed as an annular channel with substantially parallel sides, while the return channel means comprises a plurality of stationary blades, each of which is formed as a circular arc. The second stage diffuser means, on the other hand, comprises a vaned diffuser having a plurality of stationary blades, each of which is formed as a chordal portion of a cylinder; and preferably, the return channel means and the second stage 4 diffuser means are economically formed as an integrallymolded stator.

These and other objects of the present invention will become apparent from a reading of the following specification, taken in conjunction with the enclosed drawings, in which:

FIGURE 1 is a perspective view of a typical portable power-driven vacuum cleaner in which the teachings of the present invention may find particular utility;

FIGURE 2 is a top plan view thereof;

FIGURE 3 is a stepped section view, taken along the lines 33 of FIGURE 2, drawn to an enlarged scale, and showing the fan assembly of the present invention in longitudinal section;

FIGURE 4 is a transverse section, taken along the lines 44 of FIGURE 3, and showing the impeller means with a plurality of individual blades, each of which is designed as a portion of a logarithmic spiral;

FIGURE 5 is a transverse section view, taken along the lines 55 of FIGURE 3, and showing the return channel blades on the molded stator;

FIGURE 6 is a fragmentary perspective view of the molded stator, showing the return channel blades on the bottom side of the stator and the diffuser blades on its top side;

FIGURE 7 is a detail section view, taken along the lines 77 of FIGURE 3, and further showing the formation of the integrally-molded stator;

FIGURE 8 is a schematic drawing of one of the impellers of the present invention with the blades being designed in accordance with a family of logarithmic spirals characterized by a constant blade angle, the view showing the measurement of'the blade angle, the discharge angle, and the development of the absolute velocity vector, the latter representing the average absolute velocity of the air leaving the impeller in magnitude and direction;

FIGURE 9 is a schematic drawing of the assembly components-both stationary and rotaryto illustrate typically proportions between the dimensions of the various components in one preferred embodiment constructed in accordance with the teachings of the present invention;

FIGURE 10 is a typical pressure-flow (or head-capacity) curve for an embodiment of the present invention, showing a comparison with two well-known prior art devices tested under identical conditions, and further showing the requirements placed upon a typical central vacuum cleaning installation, as well as the requirements placed upon two typical industrial or commercial-type vacuum cleaners;

FIGURE 11 compares the suction unit of the present invention and that of two leading prior art commercial machines, all tested under identical conditions using an orifice tunnel, and plotting a curve of actual measured air flow at various standard orifice diameters; and

FIGURE 12 corresponds substantially to that of FIG- URE 11, but compares efiiciency versus orifice diameters.

With reference to FIGURES 1 and 2, there is illustrated a typical portable electric vacuum cleaner 10 with which the teachings of the present invention may find particular utility. It will be appreciated, however, that the invention may be used with other power-driven vacuum cleaners and is not confined to the particular cleaner 10 shown in the drawings. With this in mind, the cleaner 10 comprises a tank or receptacle 11, a base 12, a pair of wheels 13, a front caster 14, a handle 15 by means of which the cleaner may be guided, a dome-shaped cover housing 16, an inlet opening 17 in the tank, and a pair of exhaust openings 18 in the cover; and as shown more clearly in FIGURE 3, the cover houses an electric motor 19 and the fan assembly 20 of the present invention.

With particular reference to FIGURE 3, the tank supports a bag stretcher ring 21 upon which a suitable filter bag or dust bag 22 is secured. The dust bag, which is only partially illustrated, is suflicicntly porous and has an annular bead 23 to facilitate its mounting on the stretcher ring 21. The stretcher ring 21 has an annular flange 21a which receives an annular resilient gasket 24. A lower portion 25 of the cover is supported on top of the gasket and is clamped to the tank by suitable latches (not shown). The lower portion 25 of the cover is secured to the bottom of an annular peripheral rim 26 formed as part of a molded stator 27. The rim 26 has a plurality of circumferentially-spaced integrally-molded insert sleeves 28, see FIGURE 5, which are tapped to receive respective screws 29 that secure the lower portion of the cover to the stator 27. The stator is preferably integrally molded from a suitable plastic, such as a phenolic compound, primarily for reasons of manufacturing convenience and economy. An upper chamber cover 30 is secured to the stator by means of a plurality of mounting studs 31, see FIGURES 1 and 3, which receive respective lock nuts 32. The upper chamber cover 30 provides a support for the electric motor; more specifically, the motor housing cover 33 is secured to the upper chamber cover by a plurality of screws, one of which is shown as at 34 in FIGURE 3. The motor housing 35 is in turn secured to the motor housing cover 33 by means of a plurality of screws, one of which is shown as at 36. A motor skirt 37 is secured to the motor housing cover (by means of the screws 34) and the usual electric switch 38 and line cord grommet 39 are mounted on the skirt. The electrical connections between the line cord, switch, and motor are conventional and hence are omitted for ease of illustration. A motor dome 40 is secured to the top portion of the motor housing by means of screws 41.

The electric motor 19 is preferably of the universal type and comprises a field 42 (whose core is secured to the motor housing by means of screws 43) and a wound laminated armature 44 rotating concentrically within the field. The armature has a shaft 45 journaled in a bearing 46 in the motor housing cover 33. The motor is preferably of the bypass type, that is, it is provided with a sep arate air cooling circuit which is activated by a fan 47 having a hub 48 mounted on the armature shaft. The fan draws cooling air through a series of inlet ports 49, and the air is ultimately discharged through outlet ports 50. The bearing 46 for the armature shaft is retained by means of a washer 51 and screw 52, and is provided with a spacer 53 and the usual sealing gasket 54.

The fan assembly 20 of the present invention is preferably of the multi-stage type and utilizes a first stage impeller 55 and a second stage impeller 56. The impellers, which are substantially identical to one another, are mounted upon the end of the armature shaft by means of the usual spacer collar 57, washer 58, and lock nut 59, the latter engaging the threaded end 60 of the shaft.

The impellers 55 and 56, see FIGURE 4, are each provided with a plurality of blades 61; these blades 61 are designed in accordance with a family of corresponding logarithmic spirals, the purpose of which will hereinafter be explained in detail. Moreover, each impeller has a tapered lower face 62 of approximately 4, and the reasons for choosing the taper (as well as the logarithmic spiral) will hereinafter be described in detail.

The air enters a central aperture 63 in the lower portion 25 of the cover, see FIGURE 3, and into an inlet eye 64 of the first impeller 55. The purpose of the impeller 55 is to achieve an optimum transfer of the mechanical energy of the motor shaft into kinetic and pressure energy of the air. The air is discharged radially of the impeller 55 into a first stage diffuser means comprising a vaneless diffuser 65 having substantially parallel sides, the lower one of which is provided by an annular portion of the lower cover25, and the upper one of which is provided by an annular portion of a centrallyapertured circular plate 66. 'The plate 66 is secured to the underside of the molded stator 27 by rivets 67 or other suitable means. The purpose of the vaneless diffuser is to obtain a controled conversion of air velocity into pressure with a minimum of loss involved and thus to facilitate a later turn of the air back towards the axis of rotation. This turn is accommodated by the return channel means which comprises a plurality of return-channel blades 68 integrally formed as part of the molded stator 27. As shown in FIGURE 5, the return channel blades 68 are individually formed as arcuate portions of a circle. The return channel means is not intended to change the total energy level in the air, but rather, has two main functions: First, to guide the air back towards the axis of rotation and into the second impeller 56; and secondly, to minimize the losses due to turbulence in the moving air.

The air then enters into the inlet eye 69 of the second impeller 56, the design and purpose of which is substantially identical to that of the first impeller 55; and additional stages could be introduced, if desired, consonant with the teachings of the present invention. The air is discharged radially from the second impeller 56 and into a second stage vaned diffuser 70. The diffuser 70 comprices a plurality of vanes or blades 71, see FIGURE 4, which are individually for-med as chordal portions of a cylinder, with the vaned diffuser 70 being formed as part of the molded stator 27 primarily for reasons of economy and manufacturing convenience, but also, to provide an inherently smooth surface which reduces skin frictional losses. The purpose of the vaned diffuser 70 is to convert the dynamic (kinetic) energy of the air into additional static (pressure) energy to minimize the discharge losses out of the unit. The air is then discharged into an annular plenum chamber 72 formed between an annular baflle 73 and the upper chamber cover 30, see FIGURE 3; and the plenum chamber 72 is in communication with the exhaust openings 18, it being noted that the direction of the air fiow may be reversed in a suitable manner for using the vacuum cleaner as a blower.

With reference to FIGURE 8, one of the impellers (55 or 56) is shown in schematic form to illustrate the design of the impeller in accordance with the logarithmic spiral, and also, to illustrate the measurement of the blade angle and the development of the absolute velocity vector, the latter representing the average absolute velocity of the air leaving the impeller in magnitude and direction. The blade angle (denoted by 0) is the angle between the tan gent to the curve at any point and a normal to the radius of rotation at that point. The discharge angle (denoted by B) is the angle between the absolute velocity vector (denoted as V and the tangent to the outer diameter of the impeller at the blade tip. From a known derivation involving the Euler equation, it can be shown that the kinetic energy of the air leaving the impeller is dependent upon the square of V As shown by the parallelogram-type of vector diagram in FIGURE 8, V is the resultant of vector of V,,, which is the tangentail velocity of the impeller; V the so-called slip velocity of the air flow; and V the velocity of the air relative to the impeller, it being noted that V is deterrmined from V,,,, which is the normal or meridian velocity of the air and constitutes the radial component of V The logarithmic spiral is quite different from either the Archimedean spiral or the involute; and as is well known, the logarithmic spiral satisfies the polar equation:

r=polar radius to any point on the curve, a=radius of base circle,

e=base of the natural logarithm,

k=tan 0, where 0=the blade angle, and =polar angle to the same point on the curve.

The stationary components of the overall fan assembly 20 are then chosen so as to be fully compatible with the design and construction of the impellers 55 and 56. The first stage diffuser means comprising the vaneless diffuser 65, as well as the second stage diffuser means comprising the vaned diffuser 70, are formed with par- '7 allel sides for obtaining a minimum of loss, and accordingly, a maximum efliciency.

The logarithmic spiral is characterized by a constant blade angle from its inlet to its outlet portions, and this distinguishes the logarithmic spiral design from the prior art designs in which the blade angle is continually changing. A substantially constant blade angle insures a substantially uniform and optimum transfer of energy (from the mechanical energy of the motor shaft into the energy of the airdynamic and static) at the desired combination of pressure and flow and hence facilitates an improved operating efficiency of the overall fan assembly.

Moreover, as hereinbefore noted with reference to FIG- URE 3, each of the impellers 55 and 56 has a respective tapered side 62 with the taper preferably being in the order of 4 degrees and converging towards its respective straight side in a direction away from the axis of rotation. The tapered design of the impeller achieves a precise tuning in to the desired range of pressure and flow; and at the same time, improves operating efficiency, reduces back flow losses around the tip of each blade; and reduces frictional losses due to turbulence in the respective channels defined by adjacent blades.

Moreover, the blades of the impellers are inherently self-cleaning and resist the tendency for dirt to accumulate within the impeller, which is a decided improvement over the prior art practices, it being appreciated that in any vacuum cleaner, some fine dirt will eventually pass through the usual filter dust bags.

Each of the logarithmic spirals is generated from a base circle 74, see FIGURE 8, whose center coincides with the axis of rotation; a portion of the logarithmic spiral is selected, and, if desired, that portion may be approximated as closely as possible--for reasons purely of manufacturing convenienceby the arc of a circle, it being appreciated that within some region, any curve can be closely approximated by an arc of a circle.

The stationary components of the overall fan assembly 20 are then chosen so as to be fully compatible with the design and construction of the impellers 55 and 56. The first stage diffuser means comprising the vaneless diffuser 65, as well as the second stage diffuser means comprising the vaned diffuser 70, are formed with parallel sides for obtaining a minimum of loss, and accordingly, a maximum efiiciency.

Preferably, the ratio or proportion of the dimensions of the various componentsstationary as well as rotaryshould be in the following order of magnitude for optimum operating efiiciency:

Defining the inlet or inner diameter of each impeller as D see FIGURE 9, its outlet or outer diameter. as D its inlet height at H and its outlet height at H the following ratios were preferred in a typical commercial embodiment constructed in accordance with the teachings of the invention:

Moreover, the ratio of inlet area to outlet area, considered theoretically for the above noted ratios of height and diameter, equals 0.57. However, in actual practice, the blade thickness must be taken into account; and for the preferred embodiment, the ratio of inlet area to outlet area for each impeller is approximately 0.55.

It will be appreciated that these ratios are given to best illustrate to one skilled in the art how a preferred embodiment of the invention was actually constructed, that obviously, some range or latitude in dimensional proportions is contemplated, and that the above ratios are not considered as precise limitations upon the scope of the claimed invention. Moreover, these ratios may be considered as approximate values chosen for optimum operating etficiency of the system, at the required combination of pressure and flow, regardless of the particular flow is relatively high at moderate pressures.

. 8' speed of the motor shaft 45 and the actual magnitude of the physical dimensions chosen.

Further defining D, as the maximum diameter of the stator 27 (vaneless diffuser 65 as well as return channel 68) see FIGURE 9 again, D; as the maximum diameter of the inlet portion of the return channel blades 68, D as the minimum diameter of the inlet portion of the return channel blades 68 (resulting from the taper 75), D as the minimum diameter of the outlet portion of the'return channel blades 68, D; as the maximum diameter of the outlet portion of the return channel blades 68 (resulting from the oppositely-directed taper 76), D, as the inner diameter of the vaned diffuser 70, D as the outer diameter of the vaned diffuser 70, H as the height of the vaneless diffuser 65, H; as the height of the return channel blades 68, and H as the height of each vane of the vaned diffuser 70, the following ratios are appropriate:

In other words, considering the outer diameter of each impeller as unity, that is, D =1, we find in the preferred embodiment that D is 0.35; H is 0.062; H is 0.038; D is 1.52; D is 1.32; D is 1.28; D is 0.328; D is 0.40; D is 1.10; D is 1.38; H is 0.065; H is 0.077; and H is 0.055.

The head-capacity (or pressure-flow) curves of the fan assembly 20 of the present invention are shown in FIG- URE 10, along with a comparison of the corresponding curves for two leading units indicative of the commercial prior art to which the invention pertains. The efficiency curve for the entire vacuum cleaner 10 constructed in accordance with the teachings of the present invention is superimprosed upon the head-capacity curve for purposes of further illustration. The requirements of separate systems are also indicated on the curve of FIGURE 10. A system involving relatively-long lines with smaller diameters, such as may be found in a central vacuum installation, is contrasted against a system involving relatively-shorter lines, and conversely, relatively-large orifice diameters. In the first case, the pressure is relatively high and the flow is moderate; in the latter, the

In FIG- URES 10 and 11, s.c.f.m. is known in the art as standard cubic feet per minute; it is referred to as standard air at 68 F., 14.70 p.s.i.a., and relative humidity of 36%.

FIGURES 11 and 12 show the increased air fiow capacity and efficiency which is obtained with the suction unit 20 of the present invention.

To summarize, the curves of FIGURES 10, 11 and 12 demonstrate, first, that the present invention has greater air-flow capacity at useful levels of pressure or head than was heretofore available in the art; secondly, that as a result of this greater capacity, the unit covers a much wider range of typical vacuum cleaner system requirements, and this is valuable in that the same unit may be used, for example, in typical central vacuum systems as Well as in typical heavy-duty industrial applications for a portable machine;'thirdly, the peak efficiency of the suction unit of the present invention is relatively high higher than that which was heretofore obtainable in the best of the prior art machines; and lastly, the efliciency of the present invention (at the operating range) is substantially constant and is close to the peak efficiency, with the peak efiiciency falling within the operating range.

Obviously, many modifications may be made without I claim: 1. A higlrefiiciency fan assembly for a vacuum cleaner,

blower, and the like, comprising:

(A) "First and second rotating impellers, axially spaced from the one another, and having respective inlets and discharges;

(B) A vaneless difiuser comprising an annular channel radially of the first impeller discharge and communicating therewith;

(C) A stator disposed axially between the impellers and including a portion extending radially therebeyond;

(D) The stator having a pair of sides, each confronting a respective impeller inwardly of the radially-extending portion of the stator;

(E) A plurality of return channels formed on the side of the stator confronting the first impeller;

(F) Whereby the air flow is directed from the inlet of the first impeller, through the first impeller discharge into the vaneless diffuser, and beneath the radially-extending portion of the stator; and then is reversed back towards the axis of rotation, through the return channels of the stator, and into the inlet of the second impeller; and

(G) A vaned diffuser comprising a plurality of diffuser vanes formed in an annular band on top of the radially-extending portion of the stator, radially of the second impeller discharge and communicating therewith;

(H) Whereby the second impeller is nested within the diifuser vanes on the stator, and whereby the air flow from the second impeller is discharged radially through the vaned diffuser.

2. The fan assembly of claim 1, wherein:

(A) The stator with its return channels on one side and its vaned diffuser on the other side is formed integrally as a molded stator.

3. The fan assembly of claim 1, wherein:

(A) The first and second impellers are identical and comprise a plurality of circumferentially-spaced blades, each of which is designed according to a logarithmic spiral having a blade angle ranging from 32 to 38.

4. The improvement of claim 3, wherein:

(A) Each impeller has a lower tapered face, the taper converging radially away from the center of rotation. 5. In a vacuum cleaner having a receptacle tank and a cover for the tank, the combination of:

(A) An integrally-molded stator supported on top of the cover and secured thereto;

(B) A motor housing supported on top of the stator and secured thereto;

(C) A motor in the motor housing, the motor having a shaft extending coaxially through the stator;

(D) Said stator having a plurality of return-channel blades formed on one side and a plurality of diffuser vanes formed on its opposite side;

(E) First and second axially-spaced impellers mounted on the mot-or shaft with the stator therebetween, each of the impellers having respective inlets and discharges;

(F) Means directing the air flow of the first impeller discharge reversely back towards the axis of rotation and into the return channels of the stator, thence into the inlet of the second impeller; and

(G) Means directing the air flow of the second impeller discharge radially into the diifuser blades of the stator.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Centrifugal Pumps and Blowers, by Austin H. Church,

copyright 1944, pages 19, 20, 118-128; pp. 19-20 most pertinent.

MARK NEWMAN, Primary Examiner.

HENRY F. RADUAZO, Examiner. 

5. IN A VACUUM CLEANER HAVING A RECEPTACLE TANK AND A COVER FOR THE TANK, THE COMBINATION OF: (A) AN INTEGRALLY-MOLDED STATOR SUPPORTED ON TOP OF THE COVER AND SECURED THERETO; (B) A MOTOR HOUSING SUPPORTED ON TOP OF THE STATOR AND SECURED THERETO; (C) A MOTOR IN THE MOTOR HOUSING, THE MOTOR HAVING A SHAFT EXTENDING COAXIALLY THROUGH THE STATOR; (D) SAID STATOR HAVING A PLURALITY OF RETURN-CHANNEL BLADES FORMED ON ONE SIDE AND A PLURALITY OF DIFFUSER VANES FORMED ON ITS OPPOSITE SIDE; (E) FIRST AND SECOND AXIALLY-SPACED IMPELLERS MOUNTED ON THE MOTOR SHAFT WITH THE STATOR THEREBETWEEN, EACH OF THE IMPELLERS HAVING RESPECTIVE INLETS AND DISCHARGES; (F) MEANS DIRECTING THE AIR FLOW OF THE FIRST IMPELLER DISCHARGE REVERSELY BACK TOWARDS THE AXIS OF ROTATION AND INTO THE RETURN CHANNELS OF THE STATOR, THENCE INTO THE INLET OF THE SECOND IMPELLER; AND (G) MEANS DIRECTING THE AIR FLOW OF THE SECOND IMPELLER DISCHARGE RADIALLY INTO THE DIFFUSER BLADES OF THE STATOR. 